1. Field of the Invention
The present invention relates to sequencing control circuits, and more particularly to a sequencing control circuit for a south bridge chip on a motherboard of a computer.
2. Description of Related Art
A chipset is very important on a motherboard of a computer. The chipset usually includes a south bridge chip and a north bridge chip. The south bridge chip generally communicates with peripherals that include a PCI interface, an IDE controller for a hard disk or a DVD ROM drive, a USB controller, a floppy disk drive, a keyboard, and a mouse. The peripherals may be unusable if the south bridge chip is accidentally damaged due to abnormal sequencing signals.
FIG. 2 shows an example of a conventional sequencing control circuit, which has a south bridge chip 30′, a first voltage terminal 100′ being connected to the south bridge chip 30′, a second voltage terminal 300′, and a signal terminal 600′ which receives a signal generated from a power supply or a super I/O chip. The second voltage terminal 300′ is connected to the south bridge chip 30′ through a resistor R6, and the south bridge chip 30′ is also connected to the signal terminal 600′ through a resistor R7. In a normal state, the signal received by the second voltage terminal 300′ is input to the south bridge chip 30′ after the signal received by the signal terminal 600′ is input to the south bridge chip 30′ and the signal received by the signal terminal 600′ is input to the south bridge chip 30′ posterior the signal received by the first voltage terminal 100′. Thereby the signal received by the second voltage terminal 300′ is input to the south bridge chip 30′ posterior to the signal received by the first voltage terminal 100′. At this time, the south bridge chip 30′ is normal. In an abnormal state, the signal received by the signal terminal 600′ is input to the south bridge chip 30′ before the signal received by the first voltage terminal 100′, then the signal received by the second voltage terminal 300′ maybe is input to the south bridge chip 30′ before the signal received by the first voltage terminal 100′, at this time, the south bridge chip 30′ is in a state of sequencing confusion.
What is needed, therefore, is a sequencing control circuit which can ensure normal sequencing for a south bridge chip on a motherboard of a computer.